Separation of foam-forming constituents from liquids



" ms Hbifi' FIPBBOB XR 2,162,379 wnce aedrcn June 13, 1939. R, ADOLE ET AL 2,162,379

SEPARATION OF FOAM-FORMING CONSTITUENTS FROM LIQUIDS Filed June 15, 1936 Patented June 13, 1939 SEPARATION OF FOAM-FORMING CON- STITUENTS FROM LIQUIDS Richard A. Dole, San Francisco, and James W. McBain, Stamford University, Calif., assignors to Chemical Process Company, San Francisco, Calif., a corporation of Nevada Application June 15, 1936, Serial No. 85,298

14 Claims.

This invention relates to the separation of foam-forming constituents from liquids, and although not limited in its usefulness to sugar refining, will be described in connection with the removal of the surface-active non-saccharides from raw or partially refined sugar solutions.

It is a commonly observed phenomena that many substances of a colloidal nature act to increase or create the foaming ability of a liquid medium. Such substances may be referred to as foam-forming, and may easily be recognized by the simple test of putting them into a liquid medium, agitating or otherwise aerating the liquid, .and observing thercsulting foam. Without attempting an exhaustive catalog of these foam-forming substances, it may be mentioned that one of the most commonly used members of this class is soap, and that other typical members are pectin and allied pectinoid sub- 20 stances, albumin and allied albuminoid substances, water-soluble gums, s-aponin, and glycyrrhizin. It is an object of this invention to provide an improved way of separating foamforming substances from liquid media.

In the refining of sugar, the foam-forming substances which occur in the juice of the raw sugar are of especial significance since they principally constitute the impurities which are surface-active with respect to sugar, enter into com- 30 binations with the sugar, discolor the sugar and impede the crystallization. 'It is at present customary to pass partially refined sugar solutions through a bone-char filter as one of the steps in .attempting to eliminate the surfaceactive impurities; this is a slow and relatively costly step in the refining process and is in complete in its effect. Even with the best present bone-char filtering processes, there remains a substantial quantity of these surface-active im- 40 purities in the filtered solution. The concentration of these impurities in the vacuum pans retards crystallization and finally results in the production of a large proportion of low grade discolored sugar and uncrystallizable molasses, thus entailing a considerable loss. The present invention aims to provide an economical and efiicient process and apparatus for removing the foam-forming constituents (which as mentioned above are the particularly objectionable surfaceactive discolorants and crystallization retarders) from sugar solutions. Particularly it is an object of the invention to eliminate the foam-forming constituents with the minimum possible loss of sugar, or as applied to liquids other than sugar solutions, to secure a thorough separation or recovery of the foam-forming constituents from the remainder of the liquid medium.

In many cases, as in the case of sugar solutions, the foam-forming materials constitute impurities which it is desirable to remove. In 6 other cases, as in the case of licorice solutions, the foam-forming materials such as glycyrrhizin are the valuable constituents which it is desirable to concentrate and save.

The accompanying drawing diagrammatically 10 illustrates by way of example one form of apparatus for carrying out the present invention.

When applied to refining of sugar, the apparatus includes a mixing tank and reservoir H into which thesugar solution containing foam- 16 forming impurities, such as either cane juice or beet juice, continuously runs through a pipe l2.

In this tank the juice or other impure sugar-containing solution is mixed with milk of lime, continuously entering through pipe [3, in propor- 20 tions sufiicient thoroughly to break up complex compounds of the surface-acting impurities, and the sucrose of the juice. Dependent upon the quality and nature of the sugar solution, the lime added is usually between 3 and by weight of the solution, but greater or lesser amounts may be used in special cases. An excess of lime is not harmful but deficiency of lime results in incomplete purification of the sugar solution.

From the tank I I, the limed solution flows continuously through a pipe l4 into a chamber [6 provided with means for creating a foam. In its preferred form the foam-creating means consists in a false bottom 11, of a porous material such as porous alundum, or other suitable ma terial such as used in filtering and adapted to Y permit the passage of fine streams of air under pressure, and a supply of compressed air delivered by pipes l9 and I8 beneath the false bottom. In the preferred way of practicing the process of this invention the supply of sugar solution and supply of compressed air are so adjusted that substantially all of the sugar solution is converted into a mass of foam, continuously forced out of the chamber [6 by the air pressure.

At one side the foam chamber l 6 communicates with a long conduit 2|, preferably inclined, which defines a passage of travel for the foam away from its point of origin and confines it during such travel. the conduit 2| becomes filled with foam, traveling from the chamber 16 to an outlet at 22. The length of time required for foam to pass along the path of travel from chamber 16 to outlet 22 permits draining of liquid out of the foam.

In the operation of the process,

n-vI-I At the point of origin of the foam in chamber IS, the foam is composed of relatively large, thick-walled wet bubbles. As the foam progresses along the conduit 2| and more and more liquid is gravitationally separated from the mass of foam by draining out of the walls of the bubbles, the bubbles progressively become thinner-walled, smaller and drier, until finally at 22 there is discharged a very dry, fine, stable foam which hardly feels wet to the touch.

It is preferred to collect the liquid rained out of the foam separately from the liquid of chamber [6 at a plurality of places along the path of travel of the foam. Suitable fluid-collecting means for this purpose is shown as comprising a number of liquid chambers, for example four, indicated at 25, 26, 2'! and 28, each communicating at its top with the bottom of the foam conduit 2|. Liquid is thus continually collected in each of the chambers 25, 26, 21 and 28. The capacity of foam conduit 2| with respect to the amount of foam created at I6 is preferably such, as indicated above, that the foam leaving through exit 22 is very dry, which results in the liquid collected in chambers 25, 26, 2'! and 28 nearly equalling the volume of impure sugar solution entering the chamber Hi from tank H.

The liquid which separates through gravitational action by draining from the foam in conduit 2! is relatively free from the surface-acting non-saccharides which constitute the foam-forming constituents of the impure sugar solution. The foam-forming substances, such as the pectin and allied pectinoid substances, albumin and allied albuminoid substances, and, in fact, any impurity in the sugar solution tending to form a foam, will preferentially remain in the foam. Thus with the draining of relatively pure liquid from the foam, there results a concentration of the foam forming substances in the foam, so that the dry foam issuing from exit 22 is largely composed of the foam-forming substances.

The relatively pure liquid collected in chambers 25, 26, 21 and 28 might be passed to carbonating tanks such as described below without intermediate treatment, but it is preferable to treat the liquid of each of these chambers to free it from such small quantities of foam-forming ingredients as may have been entrained in this liquid by its contact with the foam in draining. Accordingly in the illustrated apparatus each chamber 25, 26, 21 and 28 is provided with foaming means preferably comprising a porous false bottom I! and a connection l8 to the air supply l9. The supply of air to each of the chambers 25, 26,21 and 28 can be much less than that to the chamber 16, since in the chambers 25, 25, 21 and 28 only a. small part of the liquid should be converted into foam. This foam thus formed in the fluid-collecting chambers 25, 26, 21 and 28 is forced out into the conduit 2| and thereby added to the main body of traveling foam.

The several liquid chambers 25, 26, 21 and 28 are shown as draining through suitable conduits 35, 36, 31 and 38 respectively to carbonating tanks 39, which may be of conventional construction and where carbon dioxide gas or some gas such as flue gas which contains carbon dioxide, from a supply 40 is passed through the liquid. The lime in the liquid is thus precipitated, and the lime precipitate drags out of solution most of the remaining non-foam-forming impurities which were not removed by the treatment described above. After passing from the carbonating tanks 39, through pipes 4| to and through filters 42, the

liquid is usually ready for the conventional vacuum pan treatment and crystallization. If further filtering is required in any. case, such further filtering can be very much reduced in extent from the bone-char filtering now commonly required in the treatment of fresh sugar juice.

Returning now to the dry foam discharged at 22, this foam contains a large amount of undissolved solid constituents, and some sugar solution, both of which it is desirable to recover. Unlike its condition when originally formed, this foam is now in condition to be subjected to mechanical separation of its liquid and solid constituents. This is accomplished by a suitable mechanical separation such for example as an Oliver filter, a filter press, a centrifugal separator, or any other kind of separator adapted to separate a relatively clear liquid filtrate from the solid constituents which constitute a sludge. In the drawing, this separator is indicated at 45, discharge sludge at 46 and relatively clear sugar solution at 41, the latter being returned to the supply of impure solution which is fed into chamber I6.

Some sludge, largely precipitated lime, may accumulate in the chamber [6, and it is accordingly preferred to pump such sludge through a pipe 48 to the separator 45. The sludge discharged from separator 45 at 46 may be retained for development as fertilizer.

It will be noted that the entire process has been described as carried out without the addition of heat. A normal cool temperature is preferred for two reasons, first, the retention of the foam-forming substances in the foam is more complete, and second, in the case of sugar, the inversion of the sugar is avoided.

We claim:

1. Process of removing foam-forming constituents dissolved or colloidally dispersed in a liquid, which comprises converting the liquid into a body of foam'in a foam-forming zone, transferring said body of foam to a foamdraining zone in which relatively purified liquid is drained from said body of foam, and segregating the drained liquid from the residual foam.

2. Process of removing foam-forming constituents dissolved or colloidally dispersed in a liquid, which comprises converting the liquid into a body of foam in a foam-forming zone, transferring said body of foam to a foam-draining zone in which relatively purified liquid is drained from said body of foam, and transferring the impuritycontaining drained body of foam to a foambreaking zone where it is broken up for disposal.

3. Process of removing foam-forming constituents dissolved or colloidally dispersed in a liquid, which comprises converting the liquid into a body of foam in a foam-forming zone, causing said body of foam to travel from said foam-forming zone through a foam-draining zone wherein relatively purified liquid is permitted to drain therefrom, entrapping the drained liquid and subjecting it to a foam-forming treatment to remove residual foam-forming constituents therefrom, conducting foam thus formed into the path of travel of the aforesaid body of foam, and removing the residual foam from said draining zone for disposal.

4. Process of removing foam-forming constituents dissolved or colloidally dispersed in a sugar solution, which comprises converting the sugar solution into a body of foam in a foam-forming zone, transferring said body of foam to a foamdraining zone in which relatively purified sugar solution is drained from the Indy of foam, and

segregating the drained sugar solution from the residual foam.

5. Process of removing foam-forming constituents dissolved or colloidally dispersed in a sugar 5 solution, which comprisesrendering the sugar solution alkaline, converting the alkaline sugar solution into a body of foam in a foam-forming zone, transferring said body of foam to a foamdraining zone in which relatively purified sugar solution is drained from said body of foam, and segregating the drained sugar solution from the residual impurity-containing foam.

6. Process of removing foam-forming constituents dissolved or colloidally dispersed in a sugar solution, which comprises converting the sugar solution into a body of foam and causing the body of foam thus formed to travel through a foam-draining zone, allowing relatively purified sugar solution to drain out of said body of foam as it travels, collecting the drained solution at a plurality of places along the path of travel of said body of foam, subjecting the solution which has collected at the several said places to a further foam-forming treatment to remove residual foam-forming constituents, and conducting the residual foam to a foam-breaking zone for disposal.

7. Process of removing foam-forming constituents dissolved or colloidally dispersed in a sugar solution, which comprises converting the sugar solution into a body of foam in a foam-forming zone, transferring said body of foam to a foamdraining zone, allowing relatively purified sugar solution to drain from said body of foam until said body of foam has changed from a relatively large and wet bubble-formation to a relatively small and dry bubble-formation, segregating the relatively purified sugar solution from the residual foam, transferring the residual foam to a foarr brealging zone, and subjecting the residual foam to mechanical separation of its liquid and solid constituents.

8. Apparatus for separating foam-forming constituents from liquids comprising means defininga foam-forming zone, means for converting a iquid in said zone into a body of foam, means defining a foam-draining zone, means operative to conduct foam formed in said foam-forming zone to said foam-draining zone, means for en- 50 trapping and segregating liquid drained from foam in said foam-draining zone, means for introducing a gaseous medium into the entrapped and segregated liquid, and means for withdrawing the drained liquid. 55 9. Apparatus for separating foam-forming constituents from liquids comprising means defining a foam-forming zone, means for converting a liquid in said form-forming zone into a body of foam, means defining a foam-draining zone along 60 which the foam can travel, means operative to conduct foam formed in said foam-forming zone to and along said draining zone, said draining zone having a plurality of pockets arranged suc- "s'tantla y cessively along the path of travel of the foam constructed and arranged to entrap drained liquid, and means for withdrawing drained liquid separately from said pockets.

10. Apparatus for separating foam-forming 5 constituents from liquids comprising means defining a foam-forming zone, means for converting a liquid in said foam-forming zone into a body of foam, means defining a foam-draining zone, means operative to conduct foam formed in 10 said foam-forming zone to said foam-draining zone, said foam-draining zone having a plurality of pockets constructed and arranged to entrap drained liquid, means for introducing a gaseous medium through drained liquid in said pockets, 15 and means for withdrawing drained liquids from said pockets.

11. Apparatus for separating foam-forming constituents from liquids comprising a closure defining a foam-forming zone, means for feeding 20 a liquid into said foam-forming zone, means at said foam-forming zone for converting liquid therein into a mass of foam, an upwardly inclined elongate chamber providing a foam-draining zone which communicates at one end with 5 said foam-forming zone, said chamber being constructed and arranged to receive foam overflowing said foam-forming zone and to conduct said foam toward its opposite end, a plurality of spaced pockets in said foam-draining zone so constructed and arranged to entrap liquid drained from foam traveling through said foamdraining zone, means in each of said pockets for foaming liquid entrapped therein, and means for draining entrapped liquid from said pockets. 35

12. A process of separating foam-forming impurities dissolved or colloidally dispersed in a liquid, which comprises converting substantially the entire body of liquid to a mass of foam, and removing by gravitational action purified liquid 40 from said mass of foam to concentrate said impurities in said mass of foam.

13. A process of separating foam-forming impurities dissolved or colloidally dispersed in a liquid, which comprises converting substantially the entire body of liquid to a mass of foam; and removing by gravitational action, independent of application of heat, purified liquid from said mass of foam to concentratae said impurities in said mass of foam.

14. A process of separating foam-forming impurities 9lXS1.. Q l 9ll lqfillxclq ll w liquid which comprises intermixing at qne logation a continuous stream of the liquid with a foam forming agent in proportions to cause sube entire body of liquid to be converted to mass ofjmtransferring said mass of foam from said location, and removing by gravitational action purified liquid from said transferred mass of foam to concentrate said 

